Glycogen Metabolism

Question 1

_____ is the major storage form of CHO in the body

Answer 1

Glycogen, found in liver, muscle (some in brain)

Question 2

1. Reaction: Glucose → Glucose-6-Phosphate (GLYCOGENESIS)

Answer 2

 Starting Compound: Glucose
 Ending Compound: Glucose-6-Phosphate

 Enzymes: Glucokinase or Hexokinase

Question 3

2. Reaction: Glucose-6-Phosphate → Glucose-1-Phosphate (GLYCOGENESIS)

Answer 3

 Starting Compound: Glucose-6-Phosphate
 Ending Compound: Glucose-1-Phosphate

 Enzymes: Phosphoglucomutase

Question 4

3. Reaction: Glucose-1-Phosphate → Uridine Diphosphate (UDPGluc) + Pyrophosphate (GLYCOGENESIS)

Answer 4

 Starting Compound: Glucose-1-Phosphate
 Ending Compound: Uridine Diphosphate (UDPGluc) + Pyrophosphate

 Enzymes: UDPGluc Pyrophosphorylase

Question 5

Process of Glycogenolysis

Answer 5

In the cytosol (muscle & liver), glycogen is broken down to glucose

Question 6

_____ (catalyzes the rate-limiting step in glycogenolysis) & cleaves 1,4 glycosidic bonds

Answer 6

Glycogen phosphorylase

Question 7

(1/2) Debranching enzyme has two catalytic sites. ______ moves a trisaccharide from one branch and places it on the other branch so the 1,6 branch point is visible.

Answer 7

Glucan tranferase

Question 8

(2/2) The second catalytic site of debranching enzyme, _____, is responsible for catalyzing the hydrolysis of the alpha 1-6 glycolytic bond that releases a free glucose.

Answer 8

1,6-glycosidase

Question 9

Reaction: Glucose-1-Phosphate → Glucose-6-Phosphate → ????

Answer 9

Free Glucose

Question 10

Glucose-6-Phosphate is found in _____ & ____

Answer 10

Glycolysis (Glucose → Glucose-6-phosphate, Glucose-6-Phosphate → Fructose-6-Phosphate)

Glycogenesis (Glucose → Glucose-6-Phosphate, Glucose-6-Phosphate → Glucose-1-Phosphate)

Question 11

Glucose-1-Phosphate is found in _____ & _____

Answer 11

Glycogenesis (Glucose-6-Phosphate → Glucose-1-Phosphate, Glucose-1-Phosphate → Uridine Diphosphate (UDPGluc) + Pyrophosphate)

Glycogenolysis

Question 12

• Glycogen synthase & Glycogen phosphorylase regulation

Answer 12

o Phosphorylation of synthase (synthase-stop) = ↓ activity

o Phosphorylation of phosphorylase = ↑ activity

Question 13

Glycogen synthase during glycogenesis

Answer 13

o ↓Phosphorylation

o cAMP ↑ phosphorylation; thus ↓ glycogen synthase

o Insulin ↓ cAMP ; thus ↑ glycogen synthase (glycogenesis)

Question 14

Glycogen phosphorylase during glycogenolysis

Answer 14

o ↑ phosphorylation
o cAMP ↑ phosphorylation; thus ↑ glycogen phosphorylase
o Insulin ↓ cAMP ; thus ↓ glycogen phosphorylase (glycogenolysis)

Question 15

_____ increases the phosphorylation of enzymes

Answer 15

Cyclic AMP

Question 16

Cyclic AMP is formed in response to ____, _____ & _____

Answer 16

epinephrine, norepinephrine (muscle & liver), glucagon (liver)

Question 17

Role of glycogen in the liver

Answer 17

provide free glucose to maintain blood concentration of glucose

Question 18

Role of glycogen in muscle

Answer 18

provide a source of G6P for glycolysis in response to ATP need for muscle contraction.

Question 19

5. Phosphorylation → Phosphorylase a = active

Answer 19

a. Glycogen phosphorylase activated by phosphorylation catalyzed by phosphorylase kinase to yield phosphorylase a

b. Allosterically inhibited by ATP and G6P in liver not muscle.

Question 20

6. Dephosphorylation → Phosphorylase b = inactive

Answer 20

a. Glycogen phosphorylase inactivated by dephosphorylation catalyzed by phosphorylase kinase to yield phosphorylase b.

Question 21

CHO Loading

Answer 21

Endurance athletes exercise to the point of exhaustion to deplete glycogen stores. Then, they consume an excess of carbohydrates to replenish glycogen stores, glycogen synthesis happens rapidly due to the lack of glycogen. This new glycogen is then used as a readily available source of fuel during intense exercise.